Tribology is a science of friction, wear, and lubrication on friction surfaces. Many different types of strain-gauges and other devices for force measuring are known in the art.
U.S. Pat. No. 4,785,673 issued in 1988 to Jean-Pierre Aumard describes a force measurement sensor for measuring at least two forces. This sensor comprises a beam with notches for imparting flexibility to the beam in the direction of action of forces to be measured. The aforementioned flexibility is required to increase reversible deformation of the beam under effect of the applied forces and thus to make it possible to measure these forces with sensing elements such as strain gauges attached to the respective deformable portions of the beam.
In the aforementioned U S. Pat. No. 4,785,673 the beam has a first pair of symmetrical transverse notches and second pair of symmetrical transverse notches at a distance from the first pair.
However, the above sensor measures two parallel forces, which are located in the same or in parallel planes. This essentially limits the field of application of the sensor. Another disadvantage of the aforementioned sensor is that the sensing elements, such as strain gauges, are arranged sequentially. As a result, the sensor has an increased overall dimension in the longitudinal direction and therefore does not possess rigidity in a force transmission direction and presents problems associated with excitation of natural frequency resonance. The natural frequency resonance, in turn, affects accuracy of measurements and limits the dynamic range of forces to be measured. Furthermore, an increased length of the sensor makes it unsuitable for measuring forced under increased temperature since the sensor is subject to significant temperature deformations.
U.S. Pat. No. 4,628,745 issued in 1986 to Yotaro Hatamura describes a multi-axis load sensor, which has radial plates adapted to detect moments produced by forces acting in planes which neither coincide nor parallel to the standard axis of at least one of the parallel plate structure. The sensor is exemplified as a device for measuring loads produced by a mechanical robot having several degrees of freedom. This sensor is more universal than the one described in U S. Pat. No. 4,785,673. However, it is still sensitive to temperature deformations and is subject to excitation of natural frequency resonance. This is because, though the load sensing elements are arranged in different non-coincident and non-parallel planes, they are still arranged in sequence and therefore the sensor has an increased length and entails the same disadvantages as the previously described sensor. Furthermore, the beam of the sensor is significantly weakened by multiple cut-outs which extend inwardly from the external surface of the beam. this is because the sensor is intended for specific application in robots which manipulate with limited forces. This limitation is an essential disadvantage of the sensor of U.S. Pat. No. 4,628,745 which makes it inapplicable for measuring large forces.